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无法将字符串转换为枚举类型

  •  0
  • Cyril Krasnobaiev  · 技术社区  · 6 年前

    public enum Language {
        EN_GB("en-gb"),
        EN_DE("en-de"),
        DE_DE("de-de");
    
        private final String text;
    
        Language(final String text) {
            this.text = text;
        }
    
        @JsonValue
        public String getValue() {
            return text;
        }
    }
    

    我有一个枚举转换类:

    public class EnumConverter {
    
        private static ReflectionFactory reflectionFactory = 
        ReflectionFactory.getReflectionFactory();
    
        private static void setFailsafeFieldValue(Field field, Object target, 
            Object value) throws NoSuchFieldException, IllegalAccessException {
    
            // let's make the field accessible
            field.setAccessible(true);
    
            // next we change the modifier in the Field instance to
            // not be final anymore, thus tricking reflection into
            // letting us modify the static final field
            Field modifiersField = Field.class.getDeclaredField("modifiers");
            modifiersField.setAccessible(true);
            int modifiers = modifiersField.getInt(field);
    
            // blank out the final bit in the modifiers int
            modifiers &= ~Modifier.FINAL;
            modifiersField.setInt(field, modifiers);
    
            FieldAccessor fa = reflectionFactory.newFieldAccessor(field, false);
            fa.set(target, value);
        }
    
        private static void blankField(Class<?> enumClass, String fieldName) throws NoSuchFieldException,
                IllegalAccessException {
            for (Field field : Class.class.getDeclaredFields()) {
                if (field.getName().contains(fieldName)) {
                    AccessibleObject.setAccessible(new Field[] { field }, true);
                    setFailsafeFieldValue(field, enumClass, null);
                    break;
                }
            }
        }
    
        private static void cleanEnumCache(Class<?> enumClass) throws NoSuchFieldException, IllegalAccessException {
            blankField(enumClass, "enumConstantDirectory");
        }
    
        private static ConstructorAccessor getConstructorAccessor(Class<?> enumClass, Class<?>[] additionalParameterTypes)
                throws NoSuchMethodException {
            Class<?>[] parameterTypes = new Class[additionalParameterTypes.length + 2];
            parameterTypes[0] = String.class;
            parameterTypes[1] = int.class;
            System.arraycopy(additionalParameterTypes, 0, parameterTypes, 2, additionalParameterTypes.length);
            return reflectionFactory.newConstructorAccessor(enumClass.getDeclaredConstructor(parameterTypes));
        }
    
        private static Object makeEnum(Class<?> enumClass, String value, int ordinal, Class<?>[] additionalTypes,
                                       Object[] additionalValues) throws Exception {
            Object[] parms = new Object[additionalValues.length + 2];
            parms[0] = value;
            parms[1] = Integer.valueOf(ordinal);
            System.arraycopy(additionalValues, 0, parms, 2, additionalValues.length);
            return enumClass.cast(getConstructorAccessor(enumClass, additionalTypes).newInstance(parms));
        }
    
        /**
         * Add an enum instance to the enum class given as argument
         *  @param <T> the type of the enum (implicit)
         * @param enumType the class of the enum to be modified
         * @param enumName the name of the new enum instance to be added to the class.
         */
        @SuppressWarnings("unchecked")
        public static <T extends Enum<?>> void addEnum( Class<T> enumType, String enumName) {
    
            // 0. Sanity checks
            if (!Enum.class.isAssignableFrom(enumType)) {
                throw new RuntimeException("class " + enumType + " is not an instance of Enum");
            }
    
            // 1. Lookup "$VALUES" holder in enum class and get previous enum instances
            Field valuesField = null;
            Field[] fields = enumType.getDeclaredFields();
            for (Field field : fields) {
                if (field.getName().contains("$VALUES")) {
                    valuesField = field;
                    break;
                }
            }
            AccessibleObject.setAccessible(new Field[] { valuesField }, true);
    
            try {
    
                // 2. Copy it
                T[] previousValues = (T[]) valuesField.get(enumType);
                List<T> values = new ArrayList<T>(Arrays.asList(previousValues));
    
                // 3. build new enum
                T newValue = (T) makeEnum(enumType, // The target enum class
                        enumName, // THE NEW ENUM INSTANCE TO BE DYNAMICALLY ADDED
                        values.size(),
                        new Class<?>[] {}, // could be used to pass values to the enum constuctor if needed
                        new Object[] {}); // could be used to pass values to the enum constuctor if needed
    
                // 4. add new value
                values.add(newValue);
    
                // 5. Set new values field
                setFailsafeFieldValue(valuesField, null, values.toArray((T[]) Array.newInstance(enumType, 0)));
    
                // 6. Clean enum cache
                cleanEnumCache(enumType);
    
            } catch (Exception e) {
                e.printStackTrace();
                throw new RuntimeException(e.getMessage(), e);
            }
        }
    } 
    

    我有例外

    java.lang.NoSuchMethodException: com.staxter.models.response.auth.Language.<init>(java.lang.String, int) at java.lang.Class.getConstructor0(Class.java:3082) at java.lang.Class.getDeclaredConstructor(Class.java:2178) at com.staxter.utility.EnumConverter.getConstructorAccessor(EnumConverter.java:61) at com.staxter.utility.EnumConverter.makeEnum(EnumConverter.java:70) at com.staxter.utility.EnumConverter.addEnum(EnumConverter.java:105)

    java.lang.RuntimeException: com.staxter.models.response.auth.Language.<init>(java.lang.String, int) at com.staxter.utility.EnumConverter.addEnum(EnumConverter.java:122)

    所以我的问题是:
    为什么我得到这个异常以及我应该在enumConverter类中编辑什么?

    3 回复  |  直到 6 年前
        1
  •  0
  •   catch32    6 年前

    如果我正确理解你的问题。要从字符串实例获取枚举类型。

    解决这个问题不需要单独的课程。
    可以使用静态方法:

    public enum Language {
        EN_GB("en-gb"),
        EN_DE("en-de"),
        DE_DE("de-de");
    
        private final String text;
    
        Language(final String text) {
            this.text = text;
        }
    
        @JsonValue
        public String getValue() {
            return text;
        }
    
        public static Language fromString(String str) {
            for (Language lang : Language.values()) {
                if (lang.getValue().equalsIgnoreCase(str)) {
                    return lang;
                }
            }
            throw new IllegalArgumentException("Illegal enum parameter: " + str);
        }
    
        public static void main(String[] args) {
            System.out.println(Language.fromString("en-de"));
            System.out.println(Language.fromString("en-gb"));
            System.out.println(Language.fromString("en-dd"));
        }
    }
    

    EN_DE
    EN_GB
    Exception in thread "main" java.lang.IllegalArgumentException: Illegal enum parameter: en-dd
        at com.tribe.pdf2data.pdf2data.dto.Language.fromString(Language.java:27)
        at com.tribe.pdf2data.pdf2data.dto.Language.main(Language.java:33)
    
        2
  •  0
  •   Oleg Cherednik    6 年前

    将工厂方法添加到枚举中。此方法将由调用 反序列化枚举。

    public enum Language {
        // ...
    
        @JsonCreator
        public static Language parseId(String text) {
            for (Lanugage language : values())
                if (language.text.equalsIgnoreCase(text))
                    return language;
    
            throw new EnumConstantNotPresentException(Language.class, text);
        }
    }
    

    作为替代方案,您可以声明 自定义反序列化程序

        3
  •  0
  •   Cyril Krasnobaiev    6 年前

    更新 我选择使用语言环境类。这对我来说更合适,也不难做我的项目。谢谢你们的提示,伙计们!